Scott Pruitt, left, administrator of the Environmental Protection Agency, with President Trump and a group of coal miners in March as the president signed an executive order that rolled back many climate-change policies.

A wolf chases magpies and ravens from an elk carcass in Yellowstone National Park in 2016. Since the mid-1990s when 31 wolves were trucked into the park from Canada, their numbers have grown and stabilized.

A photo collage of plastic fragments found in the Arctic Ocean by the research team. A study published Wednesday shows a major ocean current is carrying trillions of bits of plastic from the North Atlantic to the Greenland and Barents seas, and leaving them there.

An aerial view of the ice canyon that now carries meltwater from the Kaskawulsh Glacier, on the right, away from the Slims River. “River piracy” refers to one river capturing and diverting the flow of another.

An illustration of an extinct rat kangaroo, published in 1825. Researchers recently analyzed the costs and benefits of re-establishing and maintaining 16 species in Australia and New Zealand that went extinct in the last millennium.